1. Field of the Invention
The present invention relates to an IC (Integrated Circuit) card, and in particular, to a smart card capable of adjusting voltages supplied from an external device.
2. Description of the Related Art
An IC card being a data storage device in the form of a card is commonly used for a card terminal such as a cash dispenser or an ID (Identification) system. Further, in a GSM (Global Systems for Mobile Communication) cellular phone, the IC card is used for storing personal information and system information. Such a card terminal includes a card reader.
The IC card can be divided into a memory card and a smart card. Having only a memory for storing service information, the memory card cannot communicate with the card terminal. That is, the card terminal reads the service information written in the memory unilaterally. However, having a central processing unit (CPU) in addition to the memory, the smart card can write the service information in the memory, and change and delete the service information written in the memory. Of course, in order to access to the memory, the CPU is provided with various control signals from the card terminal. Besides, the smart card includes an input/output (I/O) unit through which it interchanges serial data with the card reader according to a protocol specified by ISO Standard 7816/1.about.3 or GSM Standard 11.11, which specifies the mechanical and electric standards for the IC card.
Referring to FIG. 1, a conventional smart card is composed of a CPU 14, an I/O unit 15, and a memory 16. The memory 16 includes a RAM (Random Access Memory) for temporarily storing information, and a non-volatile memory such as a flash ROM, a mask ROM and an EEPROM (Electrically Erasable and Programmable ROM) for permanently storing the service information. In view of the uses, the memory 16 can be divided into a program memory for storing a program for controlling an overall operation of the smart card and a data memory for storing various service information. When not used, the smart card is normally separated from the card terminal. Thus, the smart card uses the non-volatile memory to retain the service information even when it is not provided with the supply voltage from the card terminal. As is well known, the non-volatile memory can retain the information stored therein even if the supply voltage is cut off. Further, the non-volatile memory can erase unnecessary information therefrom, and read/write the service information from and into it. The CPU 14 asynchronously interchanges the serial data with the card terminal via the I/O unit 15.
In this fashion, the CPU 14 reads the service information from the memory 16 to transfer the read information to the card terminal (i.e., the card reader) via the I/O unit 15 , and writes the service information received from the card terminal into the memory 16. The memory 16 has various information stored therein, which is used when the CPU 14 accesses to the memory 16 or interchanges the service information with the card terminal via the I/O unit 15. In particular, the memory 16 stores all the service information concerning a card user, an issuer, and a sub-issuer.
FIG. 2 illustrates an arrangement of input/output contact terminals in a known smart card, as specified by GSM Standard 11.11 and ISO Standard 7816/1. Table 1 specifies the uses of the respective contact terminals C1-C8.
TABLE 1 ______________________________________ Term. Use ______________________________________ C1 Vcc (Supply Voltage) C2 RST (Reset Signal) C3 CLK (Clock Signal) C4 Unused C5 GND (Ground) C6 Vpp (Program Voltage) C7 I/O (Data I/O) C8 Unused ______________________________________
As illustrated in FIG. 2, the smart card has a number of the contact terminals which contact the card reader of the card terminal. With reference to Table 1, the contact terminals C1, C5 and C6 are related to providing the supply voltage Vcc and the program voltage Vpp to the smart card. Further, the contact terminal C2, C3, and C7 are used in transferring a reset signal RST, the serial data SD, and a clock signal CLK, respectively. Including such contact terminals C1-C8, the smart card is provided with the supply voltage Vpp from the card reader when it contacts the card reader, and consecutively initialized in response to the reset signal RST received from the card reader. After initialization, the smart card communicates with the card reader via the I/O unit 15. Here, the program voltage Vpp is applied to the flash ROM or EEPROM to permanently write the service information therein.
As is well known, the smart card operates with a specified supply voltage Vcc provided from the card reader. However, with the development of an the IC fabricating technology, there is a tendency to reduce the supply voltage (i.e., operating voltage) of the smart card. Therefore, it might happen that the supply voltage provided from an old-fashioned card reader is not coincident with the specified supply voltage of the smart card. In this case, the smart card may be damaged by the overvoltage and overcurrent. Conventionally, in order to prevent the damage, the user should check the supply voltage of the card reader inconveniently prior to use the smart card unless the card terminal has a function of automatically converting the supply voltage level.